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Title |
Limit State Evaluation of 4-Inch Steel Pipe Elbows for Low-Cycle Fatigue
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Authors |
김성완(Sung-Wan Kim) ; 윤다운(Da-Woon Yun) ; 박동욱(Dong-Uk Park) ; 장성진(Sung-Jin Chang) ; 전법규(Bub-Gyu Jeon) |
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DOI |
https://doi.org/10.11112/jksmi.2025.29.2.52 |
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Keywords |
손상지수; 피로 균열; 한계상태평가; 강재 배관 엘보; 두께 변화 Damage index; Fatigue crack; Limit state evaluation; Steel pipe elbow; Thickness change |
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Abstract |
The piping system of a nuclear power plant is composed of straight pipes and pipe elbows sequentially connected to transport fluids. Pipe elbows are an important component for absorbing the deformation and energy in a piping system. Pipe elbows are vulnerable elements in the piping system of nuclear power plants because of their low bending stiffness compared with that of straight pipes of the same material and cross-section, thus resulting in relatively large deformations. Therefore, pipe elbows require high structural integrity against seismic loads because they are important components in the piping system of nuclear power plants. Under repetitive loading conditions such as earthquakes, pipe elbows can experience significant cross-sectional plastic deformation associated with strain beyond the elastic limit of the material, which can cause the pipe elbow to failure. The most fundamental factor affecting the limit state of a pipe elbow is the structural dimensions, such as the thickness, diameter, and length of the pipe. In this study, low-cycle fatigue tests are conducted on 4-inch steel pipe elbows of schedules 40 and 80 to determine the difference in limit states due to changes in their thicknesses. The low-cycle fatigue test is conducted until leakage occurs because of fatigue cracks, which signifies the limit state of the steel pipe elbow. The limit state of the steel pipe elbow with respect to thickness change is quantitatively expressed using the damage index, which can account for cumulative damage.
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